1. Technical Field
The present invention relates to a diesel engine and more particularly a diesel engine having two combustion chambers respectively formed in a piston and communicating with each other.
2. Background Art
Various type of diesel engines have been proposed in the past. One is a diesel engine which has only one combustion chamber. Another is a diesel engine which has two combustion chambers. In both type of diesel engines, fuel is injected into the combustion chamber and self-ignition takes place therein, thereby causing combustion. The combustion process of the diesel engine is generally divided into an initial combustion process and a diffuse combustion process. The diffuse combustion process following the initial combustion process.
In the former type of diesel engines, the combustion chamber is generally formed in a top surface of a piston and fuel is injected into the combustion chamber. In the latter type of diesel engines, a main combustion chamber is formed in the top surface of the piston and another combustion chamber (which may be called a swirl chamber, an initial combustion chamber or an auxiliary combustion chamber) is formed in a cylinder head of an engine. These two combustion chambers communicate with each other by a passage formed in the cylinder head.
The one-combustion-chamber-type of diesel engine has an advantage over the two-combustion-chamber-type diesel engine in fuel consumption rate since the former does not need the passage in the cylinder head or since the passage connecting the two chambers creates a throttling loss and deteriorates the fuel consumption rate. On the other hand, the former has a disadvantage as compared with the latter in smoke (black smoke or soot) since swirl flow and squish flow produced in the combustion chamber are attenuated before and during the diffuse combustion, i.e., the former type of engines discharge a large amount of smoke or soot.
Meanwhile, there is a patent application which proposes a modified version of the two-combustion-chamber-type diesel engine (Japanese Patent Application No. 62-72433, published May 9, 1987 and owned by Fuji Heavy Industries Ltd.). FIG. 1 of the accompanying drawings shows this proposal. As illustrated in this figure, a combustion chamber 107 is formed in a top surface of a piston 103 and a swirl chamber 109 is also formed in the piston top surface. The swirl chamber 109 has a volume smaller than the main combustion chamber 107. These chambers 107 and 109 communicate with each other by a passage 111 extending from a lateral wall of the combustion chamber 107 to a lateral wall of the swirl chamber 109. The chambers 107 and 109 are also connected with each other by another passage 112 extending from a bottom of the combustion chamber 107 to the bottom of the swirl chamber 109. The second passage 112 is called a "gas injection opening" in the above patent application. Fuel is supplied from an injection nozzle 113 mounted in a cylinder head 102. The injection nozzle 113 has a larger nozzle hole 115 and a smaller nozzle hole 116. Fuel is directed into the combustion chamber 107 from the larger nozzle hole 115 and simultaneously into the swirl chamber 109 from the smaller nozzle hole 116 through the first passage 111.
In this proposal, however, fuel is injected into the combustion chambers 107 and 109 at the same time (claim 1, and specification, page 5, third paragraph, page 7, second paragraph, page 8, first paragraph of the above Japanese patent application). If the fuel is supplied to the two chambers simultaneously, combustion takes place in the smaller chamber 109 earlier than in the larger chamber 107 in most cases. Thus, gases flowing into the main combustion chamber 107 from the swirl chamber 109 can make turbulence of fuel, air and flame as well as soot in the main combustion chamber 107 at an early stage of combustion in the main combustion chamber 107. However, these gases are eventually weakened and therefore cannot maintain turbulence of air, fuel, flame and soot at a late stage of combustion in the main combustion chamber 107. Of course, swirl flow and squish flow may help make the turbulence in the main chamber 107, but these flows are also weakened gradually and little influence remains at the late stage of combustion.
Meanwhile, in the illustration, 101 designates a diesel engine, 104 an intake passage, 105 an intake valve, 106 a cylinder liner, 110 a hot plug, 114 an injection nozzle tip and 117 a connecting rod.